Question

Students in a biology class thought that salt water would affect the movements of planaria. They put 25 planaria in salt water and recorded their observations. Which flaw was present in the design of their experiment?

a - There was no hypothesis
b - There was no control
c - The sample was too big
d - The procedure was too complicated

Answer 1

The flaw present in the design of the experiment is b - There was no control. The experiment lacks a control group to compare the results of the experimental group with. The control group would be a group of planaria that are not placed in salt water, or are placed in a solution with a different concentration of salt. Without a control group, it is difficult to determine whether the observed effects on the planaria are due to the salt water or some other factor.